Refractometric Sensing of Heavy Oils in Fluorescent Core Microcapillaries

Abstract

Re´sume´-La de´tection re´fractome´trique des huiles lourdes dans les microcapillaires a`coeur fluorescents -La de´tection par re´fractome´trie d'huiles lourdes calibre´es (densite´> 1 000 kg/m 3 ) a e´te´de´montre´e à l'aide de micro-capillaires a`coeurs fluorescents. La surface interne d'un capillaire de 25 microns a d'abord e´te´reveˆtue d'une couche de silicium fluorescent a`haut indice de re´fraction (fluorescent silicon Quantum Dots, QD). Ce film de QD permet le de´veloppement de re´sonances cylindriques en mode galerie (Whispering Gallery Mode, WGM) à l'inte´rieur du capillaire. Les huiles lourdes recouvrant une gamme e´tendue de l'indice de re´fraction ont e´teí njecte´es dans le canal du capillaire, provoquant de grands changements pour les longueurs d'onde de re´sonance WGM. La sensibilite´des huiles lourdes aux indices de re´fraction les plus e´leve´s, est d'environ 250 nm par Unite´d'Indice de Re´fraction (nm/UIR), ce qui est la sensibilite´la plus e´leve´e observe´e jusqu'à pre´sent pour un capteur re´fractome´trique fonctionnant en mode fluorescent. Cela est une indication que les microcapillaires a`coeurs fluorescents pourraient eˆtre une alternative viable par microfluidique pour la de´tection chimique ou par re´fractome´trie lors des divers stades de la transformation, du controˆle et de l'utilisation du pe´trole et du gaz.Abstract -Refractometric Sensing of Heavy Oils in Fluorescent Core Microcapillaries -The refractometric sensing of calibrated heavy oils (density > 1 000 kg/m 3 ) is demonstrated using fluorescent-core microcapillaries. A 25-micron capillary channel was first coated with a high-index layer of fluorescent silicon Quantum Dots (QD). This QD film supports the development of cylindrical Whispering Gallery Mode (WGM) resonances inside the capillary. Heavy oils spanning a wide range of refractive index were pumped into the capillary channel, causing large shifts in the fluorescence WGM resonant wavelengths. The sensitivity for heavy oils approached 250 nm per Refractive Index Unit (nm/RIU) at the higher oil indices, which is the highest sensitivity so far observed for a refractometric sensor operating in the fluorescence mode. This suggests that fluorescent core microcapillaries may be a viable microfluidic alternative for refractometric or chemical sensing in various stages of oil and gas processing, monitoring and usage.

Whispering Gallery Mode Devices for Sensing and Biosensing

“…Like for microspheres [175], fluorescent capillaries can be stabilized against thermal fluctuations via control over the various layer thicknesses [176]. The highest sensitivity is reported over 400 nm/RIU for thin disks [173] and up to 250 nm/RIU for the second-order radial mode of thick capillaries with a high-index fluorescent coating [8], although values of around 10 nm/RIU are more common. The concentration detection limit for neutravidin was in the nM range [118]; considerably higher than the best results for evanescent measurements (again, illustrating the trade-offs in sensitivity vs. durability and experimental simplicity between the two techniques).…”

“…The word has two main definitions: it can refer to the use of light to control the flow of fluids, or, conversely, the applications of fluids to control the flow of light. The transition from a microfluidic WGM-type sensor to an optofluidic one was recently shown as a function of increasing analyte refractive index in the channel of a fluorescent capillary [8]. Once the fluid index exceeds that of the capillary walls, the confinement leading to the formation of WGMs is effectively within the fluid itself.…”

“…Electromagnetic resonances in these structures-the so-called "whispering gallery modes"-can be used to sense changes in the local surroundings with high sensitivity [6][7][8]. Related structures with elliptical or polyhedral cross sections can show similar effects [9][10][11][12][13][14][15][16][17][18][19], although the resonances in non-circular structures are relatively lossy due to the presence of sharp curves or corners.…”

Capillary-Type Microfluidic Sensors Based on Optical Whispering Gallery Mode Resonances

“…This is not meant as an exhaustive sampling of all such work, but simply as a brief overview to illustrate the almost limitless possibilities of refractometric capillary-based biosensing. Some studies show physical versatility of these systems, which are able to handle almost any solvent including viscous, dense oils, 86 and in many cases true chemical biosensing has been demonstrated. The most common channel wall functionalization scheme so far is based on the standard silanization reaction.…”

Microfluidic Detection of Vitamin D₃ Compounds Using a Cylindrical Optical Microcavity

“…The refractometric sensitivity is typically in the range of 5-50 nm (resonance wavelength shift) per refractive index unit (RIU) [9], [10] with extreme records in the range of 500 nm/RIU [11], [12].…”